It is known that exposure to solar radiation may have beneficial effects only if suitably controlled so as to prevent erythema, premature ageing or degeneration of a tumorous nature due to over-exposure.
In order to reduce the negative consequences of incorrect or excessive exposure to solar radiation, use is made of protective creams of varying levels which are chosen in a more or less approximate manner depending on the quality of the skin, its degree of tanning and the weather conditions, as well as the exposure time. These precautions are not sufficient in that frequently the evaluation as to the resistance of the epidermis of the person is incorrect, and also because the conditions of solar irradiation may vary greatly depending on the general atmospheric conditions. In general, a correct evaluation of the various parameters which contribute to determining the appropriate protection to be adopted is not possible owing to the part played by subjective factors.
Atmospheric pollution phenomena also make it even more dangerous to submit to ultraviolet radiation for excessively long periods, since no barrier effect against the most harmful ultraviolet radiation is provided by the ozone layer in the upper atmosphere. As is well known, this phenomenon is not noticed by the person who is exposed to the solar radiation except where this has already caused erythema or other more serious damage also affecting other organs and in particular the eyes.